A signal rise speed has increased due to an improvement in operating speed of LSIs, such as central processing units (CPUs) and, in a wiring in packages and printed boards where those LSIs are mounted and input/output signals propagate, fine wiring lines each having a width of about 1 μm to several tens of μm have come to be often used in terms of a requirement for an increase in wiring density. Inevitably, interlayer insulating films in the packages and the printed boards have also come to be required to decrease in permittivity in terms of shortening charge/discharge times.
As a technique for reducing the permittivity of an interlayer insulating film of a multilayer circuit board such as a package or a printed board, it is considered to carry out a reduction in permittivity by dispersing hollow particles or porous particles in a resin forming the interlayer insulating film or causing a large number of pores to be contained in the resin. As such a technique, Patent Document 1 discloses a method of forming a film mixed with the foregoing hollow particles or porous particles at a portion where the reduction in permittivity is to be achieved.
However, according to studies by the inventors of this invention, if a technique described in Patent Document 1 is simply applied to an interlayer insulating film forming a package or a printed board, a large number of irregularities are formed on a surface due to porous bodies, hollow particles, or pores exposed on the surface and thus, in the package or printed board wiring particularly required to be miniaturized, a problem arises which includes pattern shape failure, such as disconnection or defect, and a problem also arises that a current path in the wiring is prolonged due to irregularities caused in the wiring by the foregoing irregularities, thus leading to an increase in loss. Since Patent Document 1 refers to nothing about them and also describes nothing about a relationship between the sizes or the like of the wiring and the porous bodies to be dispersed/mixed, no solving method has been found from this document.    Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2003-323138